Known products made of composite materials incorporate threaded inserts for the fastening of components and/or structures. These inserts can be inserted in the unprocessed state between the fiber layers and worked after the cure of the resin with digital control machines, which make the holes and the threads. The precision needed by this working is extremely important since the exact position of the threaded holes must be ensured in the final product. However, this working is expensive, long and difficult to be carried out.
For overcoming this problem, WO 2006/063185 discloses inserts which are already threaded and are slipped onto smooth pins firmly fixed to the mould, after which pieces or powder of fibers are arranged and cured on the mould, so as to incorporate the threaded inserts. However, this known process does not ensure the exact arrangement in the final product and furthermore only inserts having holes which are arranged on axes perfectly parallel to the extraction axis of the product from the mould can be incorporated, otherwise this extraction would be impossible.
An and of the insert of WO 2006/063185 comprises a non-threaded cylindrical cavity coaxial to the threaded hole, while the opposite end comprises a perimetric outer ridge for preventing the insert from penetrating into the final product when a screw is screwed into the threaded hole of the insert through the end provided with the cylindrical cavity. However, only the contact between the outer surfaces of the insert and the final product prevents the insert from coming off in the opposite direction, for example if an excessive pressure is exerted during the screwing of the screw.
FR 2664529 discloses another threaded insert with a perimetric ridge, which insert is slipped onto a smooth pin which is provided with a threaded end screwed into a threaded hole of a mould, while the opposite end of the pin is provided with a washer for keeping the insert on the pin. This known pin can be unscrewed from the mould at the end of the process, however it has the above inconveniences of WO 2006/063185, in particular the imprecise axial and/or radial arrangement of the insert with respect to the mould.
Said technical problems would be particularly critical if said known inserts were employed in a process in which the fibers are grouped and arranged in overlapping layers on the mould, thus not in pieces or powder as in WO 2006/063185 or in bobbins as in FR 2664529.